Furnace systems, such as those used in residential houses, small and large buildings, and the like, are often fueled with fuels, such as oil, coal, natural gas and the like. Such furnace systems produce combustion products as flue gases which must be disposed of in the atmosphere through flue gas ductwork. One disadvantage of such furnace systems is that such flue or combustion gases retain or otherwise have a significant amount of valuable heat, and heat-producing components, derived from fuel combustion. Unless such heat, actual or potential is recovered, it escapes to the atmosphere and reduces the overall fuel efficiency of the furnace system.
Most small heating appliances, such as oil, gas and coal house heating appliances, are relatively inefficient. Typically, an oil fired home heating appliance has a maximum efficiency of between 65 to 75 percent. This means that there is a large amount of heat energy in the exhaust flue stack gases due to inefficient extraction of heat by the primary heating appliance.
It is known for example, to interpose an auxillary heat exchanger in the flue stack of a heating appliance. Typically devices designed for this purpose pass the flue gases through plain or finned tubes. A blower or some other means is provided for moving fluid such as air over the surface of the tubing and fins to effect an exchange of heat between flue gases and the air. The heated air is then recirculated back into the primary system of the heating appliance or conducted through ducts or the like to provide secondary or even primary heating of a designed space or other area.
Examples of such heat exchangers are disclosed in U.S. Pat. Nos. 4,044,950 (Aug. 30, 1977); 4,147,303 (Apr. 3, 1979); 4,291,671 (Sept. 29, 1981); and 4,342,359 (Aug. 2, 1982).
While many devices have been suggested by the prior art to improve the efficiency of heating appliances such devices are concerned with recovery of the energy in the flue stack gases and are thus directed to auxillary devises such as heat exchangers which are interposed in the flue stack of a heating appliance. Such auxillary devices are often times complex, expensive, require substantial maintenance and are often too bulky to be compatible with space requirements.
Accordingly, a desirable object of this invention is to provide a heating appliance for central or unit heating which does not require auxillary devices such as heat exchanges for efficient operation.
Another desirable object of the invention is to provide a heating appliance which maximizes efficiency while minimizing complexity and expense.
A further desirable object of the invention is to provide a heating appliance having exhaust flue gases of reduced temperatures.
A further desirable object of the invention is to provide a heating appliance having exhaust gases of sufficiently reduced temperatures whereby such gases may be vented by simple inexpensive ducting.
Other desirable objects of the invention will in part be obvious and will in part appear hereinafter.